1. Field of the Invention
The present invention relates, in part, to the papermaking arts, and specifically to the fabrics, commonly referred to as paper machine clothing, on which paper is manufactured on paper machines. The present invention also relates to the manufacture of nonwoven articles and fabrics by processes such as hydroentanglement, and specifically to the so-called industrial fabrics on which such articles and fabrics are manufactured. More specifically still, the present invention concerns the provision of such fabrics with desired functional properties through the controlled deposition thereon of polymeric resin materials.
2. Description of the Prior Art
As is well known to those of ordinary skill in the art, the papermaking process begins with the deposition of a fibrous slurry, that is, an aqueous dispersion of cellulosic fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric during this process, leaving a fibrous web on its surface.
The newly formed web proceeds from the forming section to a press section, which includes a series of press nips. The fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two press fabrics. In the press nips, the fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere its constituent fibers to one another to turn the fibrous web into a sheet. The water squeezed from the web is accepted by the press fabric or fabrics, and, ideally, does not return to the web.
The web, now a sheet, finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The sheet itself is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the web closely against the surfaces of at least some of the drums. The heated drums reduce the water content of the sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speed. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section at the downstream end of the paper machine.
The production of nonwoven products is also well known in the art. Such fabrics are produced directly from fibers without conventional spinning, weaving or knitting operations. Instead, they may be produced by spun-bonding or melt-blowing processes in which newly extruded fibers are laid down to form a web while still in a hot, tacky condition following extrusion, whereby they adhere to one another to yield an integral nonwoven web.
Nonwoven product may also be produced by air-laying or carding operations where the web of fibers is consolidated, subsequent to deposition, into a nonwoven product by needling or hydroentanglement. In the latter, high-pressure water jets are directed vertically down onto the web to entangle the fibers with each other. In needling, the entanglement is achieved mechanically through the use of a reciprocating bed of barbed needles which force fibers on the surface of the web further thereinto during the entry stroke of the needles.
Endless industrial fabrics play a key role in these processes. Generally, these fabrics are woven from plastic monofilament, although metal wire may be used instead of plastic monofilament when temperature conditions during a nonwovens manufacturing process make it impractical or impossible to use plastic monofilament. As is the case with paper machine clothing, such industrial fabrics also function in the manner of conveyors on which the webs are laid down and consolidated in a continuous fashion according to the methods described above.
In each of these situations, where a papermaker's or industrial fabric is used as an endless conveyor in a continuous production process, the inner surface of the endless fabric encounters stationary components of the machine on which it is being used and is susceptible to abrasive wear which results from such contact. To prolong the working life of the fabrics, an abrasion resistant layer of a polymeric resin material may be applied to the inner surface of the fabric. Traditionally, spraying and kiss-roll coating have been among the techniques used to apply such coatings. To their disadvantage, such techniques are imprecise and can adversely affect the permeabilities of the fabrics in a nonuniform and uncontrolled manner. As localized differences in the permeabilities can visibly affect the quality of the paper or nonwoven product produced on the industrial fabric, there has been a need for a method for applying an abrasion resistant layer of a polymeric resin material to the inner surface of an endless fabric without adversely affecting its permeability characteristics.
In a similar vein, there has also been a need to apply such a layer or coating to the outer surface of the endless fabric without adversely affecting its permeability in order, for example, to improve the handling or conveyance of the paper or nonwoven fabric being manufactured thereon. For example, U.S. Pat. No. 5,829,488 discloses a dryer fabric intended for use on a single-run dryer section on a paper machine. The dryer fabric is a woven structure having a so-called paper side which faces a paper sheet in the dryer section. At least some of the yarns of the dryer fabric on the paper side are hydrophilic to improve the adhesion between the dryer fabric and the paper sheet. The yarns may be made hydrophilic by coating the paper side with a hydrophilic polymeric resin material. It is difficult to do so by conventional methods, that is, by spraying or kiss-roll coating, without adversely affecting the permeability of the fabric.
Finally, there has also been a need for a method to apply a polymeric resin material to a papermaker's or industrial fabric in a controlled manner to adjust its permeability to a desired value either in selected regions or through the entire surface of the fabric. Such a method could be used, to remove localized departures from the uniform permeability desired for the fabric or to adjust the permeability of the fabric to some desired uniform value. For example, heretofore by changing the MD yarn count on the edges (tighter for lower permeability) verses a lower count in the center of a fabric for higher permeability, was an effort to achieve a more uniform moisture profile in the cross machine direction. This approach suffered however drawbacks.
The present invention provides for these needs by providing a method in which polymeric resin material can be applied to the surface of a papermaker's or industrial fabric at a high level of control and precision so as not to effect its permeability, and achieve a desired effect or to affect it in desired manner such as to change surface contact area, and abrasion resistance with a minimal effect on permeability or, in contrast change, void volume or localized departures of permeability.